嵌入式Linux字符设备驱动开发流程——以LED为例
1.设备模块加载及卸载
2.静态申请设备号
3.动态申请设备号
4.注册字符类设备
5.生成字符设备节点
6.完善字符类设备驱动
7.根据完善后的模板编写相关设备驱动
前言
设备驱动设备号申请分为静态申请和动态申请,本文为静态申请。
说明
静态申请需要先查看空闲设备号,不能用已使用的设备号
查看设备号命令
cat /proc/devices
头文件
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/kdev_t.h>
设备号静态申请函数
所属文件名:char_dev.c
/**
* register_chrdev_region() - register a range of device numbers
* @from: the first in the desired range of device numbers; must include
* the major number.
* @count: the number of consecutive device numbers required
* @name: the name of the device or driver.
*
* Return value is zero on success, a negative error code on failure.
*/
int register_chrdev_region(dev_t from, unsigned count, const char *name)
{
struct char_device_struct *cd;
dev_t to = from + count;
dev_t n, next;
for (n = from; n < to; n = next) {
next = MKDEV(MAJOR(n)+1, 0);
if (next > to)
next = to;
cd = __register_chrdev_region(MAJOR(n), MINOR(n),
next - n, name);
if (IS_ERR(cd))
goto fail;
}
return 0;
fail:
to = n;
for (n = from; n < to; n = next) {
next = MKDEV(MAJOR(n)+1, 0);
kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
}
return PTR_ERR(cd);
}
设备号注销函数
所属文件名:char_dev.c
/**
* unregister_chrdev_region() - return a range of device numbers
* @from: the first in the range of numbers to unregister
* @count: the number of device numbers to unregister
*
* This function will unregister a range of @count device numbers,
* starting with @from. The caller should normally be the one who
* allocated those numbers in the first place...
*/
void unregister_chrdev_region(dev_t from, unsigned count)
{
dev_t to = from + count;
dev_t n, next;
for (n = from; n < to; n = next) {
next = MKDEV(MAJOR(n)+1, 0);
if (next > to)
next = to;
kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
}
}
程序
#include <linux/module.h> //模块头文件
#include <linux/kernel.h> //内核头文件
#include <linux/init.h> //内核初始化
#include <linux/fs.h> //字符设备函数
#include <linux/cdev.h> //字符设备描述
#include <linux/kdev_t.h> //系列设备号处理宏
#define DEVICE_NAME "leds" //字符设备名称
#define DEVICE_MINOR_NUM 2 //字符设备数量
#define DEV_MAJOR 9 //主设备号
#define DEV_MINOR 0 //次设备号,0为自动分配
static dev_t leds_dev = MKDEV(DEV_MAJOR, DEV_MINOR);
static __init int leds_init(void)
{
int ret = 0;
ret = register_chrdev_region(leds_dev, DEVICE_MINOR_NUM, DEVICE_NAME);
if(ret < 0){
printk(KERN_EMERG "register_chrdev_region req %d is failed!\n", DEV_MAJOR);
}
printk("leds chrdev register is ok %d\n", ret);
return ret;
}
static __exit void leds_exit(void)
{
unregister_chrdev_region(leds_dev, DEVICE_MINOR_NUM);
printk( "leds chrdev exit \n");
}
module_init(leds_init);
module_exit(leds_exit);
MODULE_LICENSE("GPL");
编译
make
加载编译后的模块
insmod leds.ko
查看加载的模块设备号,与手动分配的设备号一致
cat /proc/devices
结束语
以上则为嵌入式Linux设备号静态申请的相关内容。
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